This patch adds puv3 pm (power management) support,
include pm device simulation for kernel booting.
Thank Blue Swirl for pointing out the missing "break".

v1->v2: Add initialization to ret in puv3_pm_read.
Signed-off-by: NGuan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>